1. Field of the Invention
The present invention relates in general to an interfacial polymerization method for preparing a non-halogenated aromatic polyesters, and more particularly to improvements in a polymerization time for a bisphenol polyarylate with along an interfacial polymerization method and a phase-transfer catalyst.
2. Description of the Prior Art
As well known to the art, aromatic polyesters produced from a mixture of terephthalic acids and/or functional derivatives thereof and isophthalic acid and/or functional derivatives thereof, and a bisphenol have many superior properties, for example, mechanical properties such as tensile strength, elongation, flexural strength, bend recovery, impact strength, physical properties such as high thermal distortion temperature, good dimensional stability, and a high heat decomposition temperature, excellent electrical properties such as inherent resistivity, dielectric breakdown strength and arc resistance. Due to these superior properties, aromatic polyesters are known to be useful in a wide range of fields as various molded articles, films, fibers and coating materials produced by injection molding, extrusion molding, press molding, and other molding techniques.
Generally, these aromatic polyesters can be prepared, for example, using an interfacial polymerization method which comprises adding an aromatic dicarboxylic acid chloride dissolved in a water-immiscible organic solvent to an alkaline aqueous solution of a bisphenol as described in J. Polym., Sci., 40, 399(1959) to W. M. Eareckson, or Japanese Patent Publication Nos. Sho. 38-3589 and 40-1959, a solution polymerization method which comprises heating a bisphenol and an aromatic dicarboxylic acid chloride in an organic solvent as described in Ind. Eng. Chem., 51, 147(1959) to A. Conix and Japanese Patent Publication No. Sho. 37-5599, or a melt polymerization method which comprises heating a polyester of an aromatic dicarboxylic acid and a bisphenol as described in Japanese Patent Publication Nos. Sho. 38-15247 and 43-28119.
It has been known that the melt and the solution polymerization method have various problems. For example, when an aromatic polyester is produced by the solution polymerization method or the melt polymerization method, a high temperature or a reduced pressure is required. In addition, the aromatic polyesters produced by the two aforementioned methods often show low molecular weights and are frequently discolored. Accordingly, the interfacial polymerization method has taken the lead recently in producing the aromatic polyesters.
According to the literature, the reagents used in the interfacial polymerization are classified into two: first, dispersing agents such as surfactants which are capable of stabilizing the reaction system, as described in detail in J. Polym. Sci., 40, 339(1959) to W. M. Eareckson and J. Macromol. Sci. Chem., A13, 875(1979) to E. Z. Casassa, D. Y. Chao and M. Henson; second, phase-transfer catalysts such as quaternary ammonium salts which are capable of activating the transfer of reactants from an aqueous layer into an organic layer, as indicated in detail in J. Macrotool, Sci. Chem., A15, 683(1981) to P. W. Morgan. For example, the latter is added to a alkaline aqueous solution containing hisphenols to activate the transfer rate of bisphenolates produced therein into an organic layer.
In accordance with other literatures, it is more effective to use a phase-transfer catalyst which has higher lypophilicity. For example, as described in J. Polym. Sci.: Part A, Vol 26, 2039(1988) to Y. D. Lee and H. B. TSAI, tetrabutyl ammonium chloride (hereinafter "TBAC"), tfiethylbutyl ammonium chloride (hereinafter "TEBAC"), and tetraethyl ammonium chloride (hereinafter "TEAC") are effective in the interfacial polymerization and because the lypophilicity of a catalyst is proportional to the number of carbon atoms contained therein, TBAC is the most effective among those. Of course, TEBAC is more effective than TEAC.
In the prior art, the quaternary ammonium salt as phase-transfer catalysts are added into an aqueous solution to produce aromatic polyesters. For example, an alkaline aqueous solution of a bisphenol containing benzyltrimethyl ammonium chloride (hereinafter "BTMAC") is used in U.S. Pat. No. 4,229,332.
However, when BTMAC is added into the aqueous layer, the concentration of bisphenolate in the organic layer is increased slowly and this increasing phenomenon proceeds continuously in even case that 60 minutes elapses. In the event of some other catalysts, the transfer rate of bisphenolate from an aqueous layer to an organic layer is relatively high, but an equilibrium state is not reached even though 60 minutes elapses. Thus, such interfacial polymerization method requires a long reaction time.
On the other hand, to make certain halogenated aromatic polyesters, an organic solution of an acid chloride containing TEBAC is used in U.S. Pat. No. 4,066,623. The authors said that their invention, which is the inverse interfacial polymerization i.e. adding the aqueous phase to the organic phase, could reduce the mount of low molecular weight fraction which accompanies the formation of these polyesters when prepared by standard interfacial polymerization techniques.
However, when this inverse interfacial polymerization is applied in polymerization method for non-halogenated aromatic polyesters, the resulting polymers were obtained in low product yield with low solution viscosity.